1/14PerformaBuilt’s Level 3 700-R4 overdrive trans handles up to 800 hp, and the company can build a 4L60E, 4L65E, or 4L70E to similar specs. The $2,695 list price includes a two-year warranty, which remains intact even if you race it.

Rocky starts are hard to shake, but the GM 700-R4 automatic has done just that. Although it promised the durability of the TH350 with the added flexibility of an overdrive when introduced in the early ’80s, savvy hot rodders immediately cried foul. Whether bolted behind a third-gen F-body, C4 Corvette, or a four-cylinder S-10 pickup, the 700-R4 quickly developed a reputation for chucking its guts. The street/strip crowd hated GM’s new automatic so much that many sacrificed overdrive altogether by swapping them out for the old TH350 or TH400. Given this kind of well-earned stigma, hearing rumors of guys putting 800 hp through these things is shocking to say the least. PerformaBuilt Transmissions (www.PerformaBuilt.com) has been beefing up these once-despised GM automatics from the very beginning, and boasts a long list of satisfied racers running 9- and 10-second e.t.’s with its 700-R4s. Needless to say, we had to take one apart to see how it’s done.

Sometimes continually refining a design that’s good enough trumps standing pat with an inherently superior product. GM played this card to perfection with both the small- and big-block Chevy engines, neither of which had a clear on-paper edge over their contemporaries. Nevertheless, incessant revisions to the cylinder head architecture and block casting technology of both platforms have enabled them to support massive horsepower and cubic inches. The same applies to the 700-R4 automatic. “Although the 700-R4 transmission wasn’t well received at first, it turned out to be a solid design with a lot of potential,” explains Alan Pickering of PerformaBuilt. “GM continually upgraded and improved the unit, and aftermarket companies jumped on the bandwagon to develop a veritable plethora of replacement components to overcome the shortfalls of the original transmission. Today we have a myriad of enhancements to choose from that enable us to produce a transmission that will hold up to 800 hp. The original unit was produced for use in 300hp vehicles, so you can see that this is quite an improvement.”

PerformaBuilt’s 700-R4 Level 3 transmission includes a modified five-pinion planetary, a heavy-duty input drum, steel pistons, Raybestos frictions and steels, a 29-element sprag assembly, a Beast sunshell, a carbon composite band, extreme-duty servos, a 13-vane pump, and a custom-built shift-improver kit. It lists for $2,695, and is backed by a two-year warranty. The same treatment is available for the 4L60E, 4L65E, and 4L80E automatics as well. Moreover, superior internals are just part of the equation. Just like you wouldn’t pair a set of cast pistons up with a big honkin’ turbo, PerformaBuilt taps into its vast experience in rebuilding the 700-R4 to match up internal components that play nice with each other. “Since our inception, our approach to building transmissions has been to maintain balance,” Pickering says. “By balancing every upgrade within the entire transmission, you never create a situation where any single component is stressed excessively. For example, when we boost line pressure within the unit, we tighten clearances and eliminate the potential for impact stress or impact shock.” Follow along as we explore the beefcake internals that make the 700-R4 a truly world-class overdrive.

Every PerformaBuilt transmission build starts with a core that is painstakingly cleaned and prepped. Instead of requiring customers to provide a core, PerformaBuilt buys its own from a select group of suppliers. Once the core has been thoroughly cleaned, the case is heated and sprayed with heat-resistant enamel paint. Heating the case allows the paint to soak in on the case surface, resulting in a more durable finish.

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While the factory 700-R4 and 4L60E used four-pinion planetary gears (right), GM incorporated a much more durable five-pinion planetary (left) into the 4L65E and 4L70E. The extra gear distributes load more evenly throughout the planetary set, dramatically improving strength. PerformaBuilt installs it into each of its 700-R4 Level 3 transmissions.

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While the stock 700-R4 rear planetary is a solid piece of hardware, it often fails due to lack of lubrication. To remedy this design flaw, PerformaBuilt cuts lubrication grooves (left) in the Sun gear to allow for improved oil flow to the rear planetary.

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Another common point of failure in the 700-R4 is the Sun gear. By using a much wider Sonnax bushing (left), PerformaBuilt significantly improves the Sun gear’s ability to endure high-load situations.

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During the evolution of the 700-R4, GM phased-in a more rugged ring gear (left) on later transmissions. The late-model ring gear is much stronger in construction and can handle far greater torque loads, which is why PerformaBuilt uses it exclusively in its Level 3 units.

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Packing the Low-Reverse clutch drum with late-model tabulated steels (left) provides enhanced lubrication. In addition to improving cooling, this also reduces drag on the clutches for reduced parasitic power loss.

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In contrast to the six-clutch setup (right) used by GM, PerformBuilt loads a nine-clutch Raybestos setup in the 3-4 drum (left). This dramatically increases the friction surface area, and results in much higher holding capability during intense 3-4 shift.

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The stock clutch drum is prone to cracking where the input shaft splines into the drum center. PerformaBuilt installs a Sonnax billet sleeve to reinforce this area. The added strength virtually eliminates cracking.

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The 700-R4's center support bears the full load of a hard launch. Unlike the early-model sprag-type center supports (left), the later-style units use a mechanical diode design for much greater durability.

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The Sun shell endures the driveline shock that ensues on the 1-2 shift, and is yet another notorious weak link on the 700-R4. To address the situation, PerformaBuilt’s Level 3 trans features a Sonnax “Beast” Sun shell (left) that is built from much thicker metal.

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When subjected to abuse, the stock 2-4 band (left) slips or breaks off at the pin. For extra holding capacity, the PerformaBuilt Level 3 trans uses a carbon composite band that is 25 percent wider. It also has a reinforced pin pocket to prevent breakage. When matched with a Sonnax Super Servo, the result is much greater holding power in Second and Fourth gears.

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Keeping fluid circulating through the trans is critical to proper operation and longevity. PerformaBuilt adds hardened rings and Teflon bushings to the pump, as well as a .500-inch Sonnax boost valve, for increased line pressure.

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The final piece of the puzzle is customizing the valve body for optimal performance. While PerformaBuilt is mum on how exactly they set up their valve bodies, suffice it to say that the passages have been modified for quicker, firmer, and more progressive shifts. The goal is for the trans to provide crisp shifts under normal driving, and quicker and harder shifts as throttle input increases.